Children born outside the United States have a lower risk of allergies including asthma and eczema, a study says.
Moving to the U.S. also increases risk of developing an allergy. According to the researchers, the risk of certain allergies among foreign-born children increases after they have lived in the U.S. for about a decade.
The research was published in the Journal of the American Medical Association and conducted by scientists at St. Luke's-Roosevelt Hospital Center in New York.
Foreign-born Americans have significantly lower risk of allergic disease than U.S.-born Americans. However, foreign-born Americans develop increased risk for allergic disease with prolonged residence in the United States," wrote Dr. Jonathan Silverberg, of St. Luke's-Roosevelt Hospital Center in New York, and colleagues in a journal news release.
Scientists looked at records and conducted phone surveys of almost 92,000 people in the U.S. They looked at several allergies including asthma, eczema, hay fever, and food allergies such as a peanut allergy. The study found children born outside the United States had significantly lower prevalence of any allergic diseases at 20.3 percent than those born in the United States at 34.5 percent.
Additionally, foreign-born children tended to have allergies such as hay fever or eczema but not food allergies or asthma.
The rate of allergies in the U.S. has been steadily increasing. According to the American Academy of Asthma Allergy and Immunology, one in 12 people in the U.S. (25 million) had asthma in 2009, compared with 1 in 14 (20 million people) in 2001. Allergies are essentially a symptom of a very sensitive immune system as it reacts strongly to an otherwise harmless substance.
What's the cause? One of the leading theories as to the rising rate of allergies blames our environment. Called the "hygiene hypothesis," experts believe a lack of exposure to germs prevents our bodies from naturally building up our immune systems.